This invention relates to cylinder head gaskets for internal combustion engines. In particular it is concerned with metal-elastomer gaskets of the kind wherein a metal core sheet is provided with a plurality of apertures corresponding to engine cylinder bores, oil and/or water passageways and the like, the margins of these apertures being provided with individual sealing elements in the form of metal eyelets and elastomer seals.
The elastomer seals used in this type of product usually take the form of edge or surface moulded elastomer material. The use of an elastomer or other coating on a steel core sheet is also known. In order to achieve satisfactory sealing using elastomer coatings or elastomer beads it is desirable to compress the elastomer coating or bead so as to achieve a total height reduction of from 20-30%. But at the same time it is necessary to seal around combustion chamber apertures where elastomer seals are unsatisfactory, due to the temperatures and pressures to which combustion chamber seals are subjected in use.
One solution to the cylinder bore sealing problem is the use of metal eyelets inserted into the cylinder bore apertures. These function also as compression limiting stops facilitating control over the compressive forces applied to any elastomer seals on the gasket, but the use of eyelets in this way can lead to various kinds of structural distortion in the engine, due to inadequate gasket conformability. Another proposal is the use of at least one annular corrugation surrounding each of those gasket apertures where no elastomer seal is desired. Alternatively wire rings may be used. The use of corrugations and wire rings is commonly combined with the use of eyelets, the latter enclosing the corrugation or wire ring, the purpose of which is to impart a degree of resilience to the metal-to-metal interface.
More recently it has been proposed to construct gaskets with a metal core sheet which is actually made up from a plurality of relatively thin metal sheets; typically three layers are used, but up to five or more layers may be used. The individual sheets may be coated to enhance sealing performance; gas sealing around cylinder bore apertures is accomplished by embossing into at least one of the sheets a corrugation which on compression between a cylinder head and block is progressively and to some extent resiliently flattened between the latter parts to develop a sealing pressure around the aperture in question.
The use of a corrugation as a cylinder bore seal is well-known, particularly with the use of a metal eyelet which overlaps and encloses the corrugation. In heavy duty applications, such as diesel engines, it may be necessary to use a relatively thick metal core which requires considerable force to be used to compress the corrugation, far more than is needed to develop a satisfactory seal at other apertures where elastomer beads constitute the sealing means. An object of the present invention is to provide an improved eyelet for use in a gasket of this kind. It is a further object of the invention to provide a gasket embodying this improved eyelet.